Clarify "DAG dependency order" in docstrings

[Yoshanuikabundi]

Fixes #223

[pep8speaks]

Hello @Yoshanuikabundi! Thanks for opening this PR. We checked the lines you've touched for PEP 8 issues, and found:

• In the file gufe/protocols/protocoldag.py:

Line 66:80: E501 line too long (80 > 79 characters) Line 163:80: E501 line too long (80 > 79 characters)

[codecov[bot]]

Codecov Report

All modified lines are covered by tests :white_check_mark:

Comparison is base (dcc7896) 99.18% compared to head (ad6f345) 99.18%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #244 +/- ## ======================================= Coverage 99.18% 99.18% ======================================= Files 36 36 Lines 1838 1838 ======================================= Hits 1823 1823 Misses 15 15 ``` | [Files](https://app.codecov.io/gh/OpenFreeEnergy/gufe/pull/244?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=OpenFreeEnergy) | Coverage Δ | | |---|---|---| | [gufe/protocols/protocoldag.py](https://app.codecov.io/gh/OpenFreeEnergy/gufe/pull/244?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=OpenFreeEnergy#diff-Z3VmZS9wcm90b2NvbHMvcHJvdG9jb2xkYWcucHk=) | `100.00% <ø> (ø)` | |

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